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VoIP Protocols: A Closer Look

A VoIP protocol is a set of rules or procedures that needs to be followed to allow an orderly communication, and determines the type of error checking and data compression that should be used, as well as how the sending and receiving devices should indicate that they have finished sending or receiving the message.  There are a variety of protocols that can be used to complete a VoIP phone call, but the most commonly used protocols in the industry include:

  • H.323:  H.323, a binary based protocol, allows users to establish multimedia communication (audio, video, or other data communication).  H.323 has a number of features that handle failure of network entities, including “alternate endpoints” and “alternate gatekeepers”.
  • Session Initiated Protocol (SIP):  SIP has replaced H.323 to a large degree.  It carries out signaling by sending small messages, consisting of a head and a body.  A SIP message carries a lot of information which helps identify the session, control timing, and describe the media.
  • Real-time Transport Protocol (RTP): RTP is used extensively in communication and entertainment systems that involve streaming media.  RTP is used in conjunction with the RTP Control Protocol (RTCP).  While RTP carries the media streams, RTCP is used to monitor transmission statistics and quality of service and aids synchronization of multiple streams.
  • Session Description Protocol (SDP): SDP does not deliver media itself, but is used for negotiation between end points of media type, format, and all associated properties.  SDP is designed to be extensible to support new media types and formats.  SDP is commonly used in conjunction with RTP and SIP, or as a standalone format.
  •  H.248: H.248 is also known as Gateway Control VoIP Protocol, and is standard protocol for controlling the elements of a physically decomposed multimedia gateway, which enables separation of call control from media conversion.  It is used to separate the call control logic from the media processing logic in a gateway.
  • Skinny Client Control Protocol (SCCP):  SCCP is a lightweight protocol for session signaling with Cisco Unified Communications Manager.  This acts as a signaling proxy for call events initiated over other common protocols such as H.323 or SIP.

With the use of various protocols determining the type of error checking and data compression methods being used to deliver the message, as well as various codecs encoding and decoding the message, VoIP and VoIP Protocol is a secure way for voice to be transmitted.

To learn more about VoIP, VoIP Protocol and how it works, visit the following posts:

VoIP: What is it and How Does it Work?
Understand VoIP: Codecs and Protocols


David Wise

David Wise

Chief Executive Officer, Founder at AVOXI
David has more than 18 years of management experience in the telecommunications industry. A graduate of the Citadel, David worked as a Senior Account Executive with Intermedia Communications and later co-founded Rapid Link, a leading provider of International callback and VoIP. David then founded AVOXI in 2001with a focus on providing niche international call center markets with customized voice and data services. read more
David Wise
David Wise

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